Walk outside, put your face up and wait a while. If your face gets wet
slowly, it's a drizzle. If your face get wet like in a shower, it's
pouring.

:)
Sorry could not resist, it's Friday again.

Water conducts electricity. Make a sensor with a PC board that has two
tracks in a Zig-Zag fashion about the size of a match box. Connect the
one track to +V and measure the Vdrop on the other. The lower the Vdrop,
the more water is on the sensor.
Of course, you will have to keep this clean and you also have to wait
for the sensor to dry before you can make another measurement.
Just a nutshell, I have not done this yet, but thought about it one time
or another.

Put the board in 60° angle so that the water pours down from the
board. Also, the distance between the tracks should be less than the
size of a water drop.

Juan Jimenez

Water conducts electricity. Make a sensor with a PC board that has two
tracks in a Zig-Zag fashion about the size of a match box. Connect the
one track to +V and measure the Vdrop on the other. The lower the Vdrop,
the more water is on the sensor.
Of course, you will have to keep this clean and you also have to wait
for the sensor to dry before you can make another measurement.
Just a nutshell, I have not done this yet, but thought about it one time
or another.

In message <37175616.9A4768A0KILLspamarrakis.es>, Tini Socas
<.....esocasKILLspam.....ARRAKIS.ES> writes
>Hello,
>
>I need make a rain detector,
>Any idea??
Use a sheet of glass with an IR emitter and detector arranged on the
underside so the beam is reflected by the glass, any water falling on he
glass will affect the refractive index thus bending the beam and
breaking the IR path. Alternatively, mount a pic based altitude sensor
onto a convenient local cow, work out the average altitude of the cow
and if the altitude is lower than the average for any significant length
of time the cow is either lying down, thus signalling impending rain, or
dead, in which case you need to go outside and find a new cow, therefore
enabling you to see if it's raining.
--
Clint Sharp

At 11:30 AM 16/04/99 -0600, you wrote:
>Let be a little serious for a moment.
>
>Sprague used to make a very nice fluid detector, was pretty cheap, and you
>just used a couple of probes and it generated the AC current for them.
>Suppose you could use PWM maybe?
>
>It depends on if you want to detect moisture or measure a level...ie....its
>raining hard enuf not to turn on the sprinklers

We are looking at rain detectors at present. One simple way is to use 2
wires and look at conductivity changes. However, we need to detect rain
very quickly and protect a field instrument and also as soon as rain is
finished we need to re-enable the instrument again. This brings in all
sorts of problems. With conductivity it is amazing how long a drop of water
will stay on 2 electrodes.

At 12:59 PM 16/04/99 -0500, you wrote:
> Put the board in 60¡ angle so that the water pours down from the
> board. Also, the distance between the tracks should be less than the
> size of a water drop.
>
> Juan Jimenez
>
>Water conducts electricity. Make a sensor with a PC board that has two
>tracks in a Zig-Zag fashion about the size of a match box. Connect the
>one track to +V and measure the Vdrop on the other. The lower the Vdrop,
>the more water is on the sensor.
>Of course, you will have to keep this clean and you also have to wait
>for the sensor to dry before you can make another measurement.
>Just a nutshell, I have not done this yet, but thought about it one time
>or another.
>
>Quentin
Try this and you will find water droplets sticking between the tracks. You
can use some form of spinning to centrifuge the water away but this brings
in other problems.

The best solution I ever saw is simple as a pure resistor dissipating
power.
Just make a resistors bridge, 4 x 560 ohms, three resistors packed in
epoxy and protected from rain, just one exposed to the environment
(rain). All resistors assembled close to each other. Measuring the delta
voltage between the two middle points of the bridge would tell you if
the exposed resistors is dissipating temperature faster, it means it is
exposed to water. Ambient temperature also changes the voltage, but the
other resistors also receive it through the epoxy.

It is quite easy to do the experiment at home. Just 4 resistors and an
ohm-meter.

Use an IR led and a lens to spread the beam out so it is an inch wide. Then
have a second lens to focus this beam back onto an IR phototrans which is
somewhat sheilded from visible light (one of the ones with a dark filter on
it). Modulate the IR beam and use synchronous detection on the other end.
Position the emitter/lens system opposite the detector/lens system,with an
inch between them. Have a large funnel to collect rain and channel it
between the two lenses. Look at the output of the synchronous detector and
look for high frequency changes (> a few Hz). If you see such noise, it has
to be something falling in between the sensors, most likely rain. You might
also want to angle the optical axis with respect to the vertical so that
not only would water change the transmission,but the refraction of the
air/water/air path would divert some of the IR away from the detector.

>At 12:59 PM 16/04/99 -0500, you wrote:
>> Put the board in 60¡ angle so that the water pours down from the
>> board. Also, the distance between the tracks should be less than the
>> size of a water drop.
>>
>> Juan Jimenez
>>
>>Water conducts electricity. Make a sensor with a PC board that has two
>>tracks in a Zig-Zag fashion about the size of a match box. Connect the
>>one track to +V and measure the Vdrop on the other. The lower the Vdrop,
>>the more water is on the sensor.
>>Of course, you will have to keep this clean and you also have to wait
>>for the sensor to dry before you can make another measurement.
>>Just a nutshell, I have not done this yet, but thought about it one time
>>or another.
>>
>>Quentin
>Try this and you will find water droplets sticking between the tracks. You
>can use some form of spinning to centrifuge the water away but this brings
>in other problems.
>
>Peter
>
|

Install a protected microphone inside an weather resistant thin metal
box or can, install the box in 45¡ to not accumulate dirt or water on
top of it, glue some small "antenas" 5" long on top of it to avoid birds
to ... stay there.

Even small water drops would make noise when falling over the can,
amplify the mic signal and "voila", you have a "sound rain sensor". I
bet that not even a noisy cricket would trigger the sound level
generated by rain drops. Except if you live close to an air force
strip, or in Florida, with those heavy sonic booms, but even so, you can
count at least 3 to 5 heavy pulses to close your equipment. You could
use a low pass filter to get only the rain drops sound...

Who does not remember those old cans on the rain, perfect sleepy time,
and we can hear it far away...

Today finally rain in Orlando, after several weeks and severe fires
burning several houses and trees all around. With all the respect for
those who lost their houses and memories, lets get to the point:

Observing the fine rain drops, they almost float with the wind. If a
little smaller they would probably land without any "bump" into the
surface, just depositing itself by mass attraction or by high relative
humidity, and hydrogen connection. Don't forget about heavy moisture or
fine fog. It means that your equipment can be exposed and completely wet
without a single sound generated at the sound transducer. Probably you
would need to use both techniques, sound and electric/thermal
conductivity.

Ok, my final considerations for the thermal:

Use two "zebras" or "combs" to increase the area to receive the rain
drops and measure the electric current between the two elements in the
zebras. Once some current is measured, it means "rain", turn on a
small heater (few resistors) below the zebra to heat and dry it, so no
water would be deposited there for long. The problem is that it
requires cleaning, wet and dry, stick dust forming an electric bridge
between the "combs", don't trust rain to "wash clean" the combs. Some
electrolysis corrosion (even with AC?) can occur if evapolating water
drops with electric current (I guess).

Probably the resistor bridge is the most practical and reliable, even in
fine and small fog or spray it should works fine. You can build the
bridge with several resistors in series/parallel to increase the
receptive sensible area.

Years ago I needed a 3 x 4" small dissipative plate. We produced it with
a mix of epoxy and graphite (carbon) from several pencils, mixed well,
molded, leads inserted and waited to dry. Something like that (tickness
less than 2 mm) could be produced as a water sensor by thermal transfer
in the bridge. Probably a flexible plate could be done using silicone
glue, but I am afraid silicone would isolate the small grains of carbon
due to its molecular structure, it doesn't mix very well with other
things. The protected resistors should match the exposed resistance for
a try zero balance with no rain. White or not so dark epoxy and a thin
white painting would reduce sun heating, but it is not totally
necessary, since heat and rain change the resistance in opposite
directions, so easy to discriminate.

The use of any kind of water concentration or funnel is not recommended
because fog or fine spray would take longer time to concentrate and drop
water over the resistor, and your equipment would be all wet already.

Would using a thermistor as a self-heating device, make sense here?
Then you'd in effect have a "wet bulb" thermometer potentially, and
you'd get a larger resistance change, potentially, with less current.
Just a possible optimization of the same idea. This might prevent the
need for conductance Combs etc.

On sound, detecting thunder chould be a consideration, it's likely to
mean it's time to cover the equipment <G>

Mark

Wagner Lipnharski wrote:
> <snipped>
> Probably the resistor bridge is the most practical and reliable, even in
> fine and small fog or spray it should works fine. You can build the
> bridge with several resistors in series/parallel to increase the
> receptive sensible area.
> <snipped>

Well, going to the side of rain preview, it could be interesting... :)
Like air static charge, change in the wind temperature, barometric
pressure, sun radiation change with sudden darkness level, and so on...

As the wind before rain is mostly caused by the heavy masses of falling
water and drastic temperature variations, it also carries the
characteristic odor of soil mixed with ozone, people use to say "you can
smell rain before it happens"...

Also, few photo-diodes pointing to different angles at the sky, could
generate a pattern of different (but not so much) light intensities.
When a dark rain comes from somewhere, the sky in that direction goes
nastly black with a severe change in the photo-diodes comparison...

It is possible to use several sensors, as we actly do, feeling rain
drops, smell, visual, thunders sounds, and so on... :)

The thermistor idea is good, since it amplifies the effect of thermal
transfer / resistance variation.

>
> Would using a thermistor as a self-heating device, make sense here?
> Then you'd in effect have a "wet bulb" thermometer potentially, and
> you'd get a larger resistance change, potentially, with less current.
> Just a possible optimization of the same idea. This might prevent the
> need for conductance Combs etc.
>
> On sound, detecting thunder chould be a consideration, it's likely to
> mean it's time to cover the equipment <G>
>

Peter Grey wrote:
>
> At 11:30 AM 16/04/99 -0600, you wrote:
> >Let be a little serious for a moment.
> >
> >Sprague used to make a very nice fluid detector, was pretty cheap, and you
> >just used a couple of probes and it generated the AC current for them.
> >Suppose you could use PWM maybe?
> >
> >It depends on if you want to detect moisture or measure a level...ie....its
> >raining hard enuf not to turn on the sprinklers
>
> We are looking at rain detectors at present. One simple way is to use 2
> wires and look at conductivity changes. However, we need to detect rain
> very quickly and protect a field instrument and also as soon as rain is
> finished we need to re-enable the instrument again. This brings in all
> sorts of problems. With conductivity it is amazing how long a drop of water
> will stay on 2 electrodes.

This is just an idea, but why not boil it off with a high
current? I suppose it won't be battery-friendly then...

Following is copied from DS web site:
------------------------------------------------------------
---------------------------------
Rainfall
Rainfall is commonly measured with the fill-and-tip method.
Rain enters the collector, drips through a small hole in its
funnel-shaped bottom, and falls into one of two identical
receptacles of known volume mounted on either end of a beam.
One vessel is up, the other down. When the upper receptacle
is full, that end of the beam pivots down. The water spills
out and drains away. This action raises the lower receptacle
into the up position and the cycle continues. Each time the
beam moves, a magnet mounted to it momentarily closes a reed
switch, with each closure typically representing 0.01 in. of
rain. Because the system incorporates a DS2423 1-Wire
counter chip with the reed switch, rainfall measurement
capability can be added to the weather station by simply
connecting its I/O pin to the twisted-pair bus.
------------------------------------------------------------
---------------------------------
Gary

<BIG SNIP>
>
>This is just an idea, but why not boil it off with a high
>current? I suppose it won't be battery-friendly then...
You are exactly right and we are trying to minimise power consumption as
much as possible. This just happens to be going into a tropical area for
testing initially and it is located on the coast (seagulls!!).